Health insurance, private health insurance, medical insurance, comprehensive medical insurance – they are all names for the same kind of insurance cover. They all suggest that the policy holder will be protected against the financial cost of medical bills, allowing them rapid access to whatever treatment is required and the choice of when that treatment is delivered.

Rarely, however, can any insurance cover be so open-ended and health insurance is no exception. Like most insurance, private medical insurance also has its fair share of exclusions that can catch some people out when they discover that their insurer declines to pay for some treatment that they had imagined would be covered.

Indeed, in a 1998 report on private medical insurance generally, the Office of Fair Trading was somewhat critical of the wide range of policies that offered different levels and types of cover to their respective policyholders. In response to this criticism, the Association of British Insurers published some useful guidelines – Are you buying private medical insurance? – which set out what it described as "core product" features that most insurance plans should offer and an explanation of the most common types of exclusion.

The core product features of most health insurance, therefore, should include cover for:

- Treatment of acute medical conditions (where and acute condition is defined as "a disease, illness or injury that is likely to respond quickly to treatment which aims to return you to the state of health you were in immediately before suffering the disease, illness or injury which leads to your full recovery");

- Surgery;

- Hospital accommodation and nursing care; and

- In-patient tests and procedures.

When it comes to the exclusions from this core product, these are defined by a term that will be familiar to anyone who has arranged any type of insurance that involves any form of medical health; namely "pre-existing conditions".

Although policies will differ in their detail (and should therefore be considered carefully before committing to a particular health plan), the general definition of a pre-existing condition is one for which the policyholder received treatment or suffered symptoms generally within 5 years of applying for the insurance. Under the majority of policies, the insurer will simply decline to meet the cost of any treatment for such conditions. With other policies, however, a so-called "moratorium" is applied. Although no cover is available for the pre-existing condition during the first two years of the policy, if the policy holder has been free of any such pre-existing condition during this two-year period, the insurer will pay for its treatment after the two-year "moratorium".

In a similar vein, the distinction between "acute" (as described above) and "chronic" is relevant. Chronic conditions are those that require repeat treatment over a length of time. Such chronic conditions are also excluded from the health insurers' core product and patients seeking private treatment would have to pay for that treatment themselves.

Treatment in NHS accident and emergency departments is excluded from medical insurance plans, but any subsequent transfer, because of extended hospitalisation is likely to be covered.

Private health insurance will also commonly exclude the need for any treatment arising from pregnancy or childbirth.